Activated carbon is commonly used for the removal of organic contaminants from aqueous waste streams. It is frequently observed that carbon beds provide an excellent medium for microbial growth. This bioactivity is often regarded as a nuisance, although in many cases improvements in reactor performance are also noted. Some research attention has been devoted to intentionally operating carbon columns as combined bio/physico/chemical treatment system, mostly for municipal wastewater treatment. this proposal is based on the premise that activated carbon columns can be designed and operated for the treatment of contaminated groundwater supplies so that the processes of biodegradation and adsorption complement each other to provide treatment performance superior to that obtainable by either process alone. Experiments will be performed to evaluate the design and operational parameters affecting biological activated carbon systems, and to identify the mechanisms operative in such systems. This research is designed to lead to improved and less expensive treatment systems for hazardous waste site remediation.